The incorporation of electronic devices with pneumatic tire structures yields many practical advantages. Tire electronics may include sensors and other components for relaying tire identification parameters and also for obtaining information regarding various physical parameters of a tire, such as temperature, pressure, number of tire revolutions, vehicle speed, etc. Such performance information may become useful in tire monitoring and warning systems, and may even potentially be employed with feedback systems to regulate proper tire pressure levels.
U.S. Pat. No. 5,749,984 (Frey et al.) discloses a tire monitoring system and method that is capable of determining such information as tire deflection, tire speed, and number of tire revolutions. Another example of a tire electronics system can be found in U.S. Pat. No. 4,510,484 (Snyder), which concerns an abnormal tire condition warning system. U.S. Pat. No. 4,862,486 (Wing et al.) also relates to tire electronics, and more particularly discloses an exemplary revolution counter for use in conjunction with automotive and truck tires. Examples of aspects of tire pressure monitoring systems are disclosed in U.S. Pat. No. 4,004,271 (Haven et al.), U.S. Pat. No. 4,742,857 (Gandhi), U.S. Pat. No. 5,616,196 (Loewe), and U.S. Pat. No. 5,928,444 (Loewe et al.).
Yet another potential capability offered by electronics systems integrated with tire structures corresponds to asset tracking and performance characterization for commercial vehicular applications. Commercial truck fleets, aviation crafts and earthmover/mining vehicles are all viable industries that could utilize the benefits of tire electronic systems and related information transmission. Tire sensors can determine the distance each tire in a vehicle has traveled and thus aid in maintenance planning for such commercial systems. Vehicle location and performance can be optimized for more expensive applications such as those concerning earth mining equipment. Entire fleets of vehicles could be tracked using RF tag transmission, exemplary aspects of which are disclosed in U.S. Pat. No. 5,457,447 (Ghaem et al.).
Such integrated tire electronics systems have conventionally been powered by a variety of techniques and different power generation systems. Examples of mechanical features for generating energy from tire movement are disclosed in U.S. Pat. No. 4,061,200 (Thompson) and U.S. Pat. No. 3,760,351 (Thomas). Such examples provide bulky complex systems that are generally not preferred for incorporation with modern tire applications. Yet another option for powering tire electronics systems is disclosed in U.S. Pat. No. 4,510,484 (Snyder), which concerns a piezoelectric reed power supply symmetrically configured about a radiating center line of a tire.
Another typical solution for powering tire electronics systems corresponds to the use of a non-rechargeable battery, which inherently provides an inconvenience to the tire user since proper electronics system operation is dependent on periodic battery replacement. Conventional batteries also often contain heavy metals that are not environmentally friendly and which present disposal concerns, especially when employed in highly numerous quantities. Still further, batteries tend to deplete their energy storage quite rapidly when powering electronic applications characterized by complex levels of functionality. Battery storage depletion is especially prevalent in electronic systems that transmit information over a relatively far distance such as from truck wheel locations to a receiver in the truck cabin. Even when batteries are used in electronics systems that transmit from wheel locations to a closer receiver location, information is then typically relayed via hard-wire transmission medium from the RF receiver location to the vehicle cab thus requiring the installation of additional and often expensive communications hardware in a vehicle.
Yet another known method for deriving power for tire monitoring systems relates to scavenging RF beam power with an interrogation antenna in close proximity to a tire and integrated electronic features. Energy that is radiated from the antenna is scavenged to power the electronics, which must often be very specialized ultra-low-power electronics limited to within a few microwatts. Interrogation antennas employed in conjunction with beam-powered electronics must typically be placed in relatively close proximity (within about two feet) to each wheel well due to limited transmission ranges. This typically requires multiple interrogation antennas per vehicle, thus adding to potential equipment costs. Each antenna is also quite susceptible to damage from road hazards, and thus for many reasons may not be the most desirable solution for powering certain tire electronic applications.
Many known methods for harvesting power and providing power to tire electronics systems exist. However, aspects of such known technologies may be undesirable in certain tire applications. As such, it is desirable to provide an improved method for harvesting electric power for tire electronics applications.
In further accordance with the present subject matter, it is appreciated that certain electrical properties are inherently associated with tire structures. For instance, moving vehicles and tire assemblies provided in conjunction thereto experience a build-up of static electricity. Unless a grounding path is provided, moving vehicles experience a build-up of static electricity that can be of relatively high voltage. Such charge build-up is undesirable for a number of reasons. For example, the presence of such a charge can produce a source of interference for and thus an adverse effect on the vehicle's electronic circuitry including radio reception. Excess charge can also create a spark potential that can present a safety hazard during refueling. Furthermore, the grounding of a charge through a vehicle occupant, typically upon entering or exiting the vehicle, can be particularly uncomfortable.
Tires can be used to provide a ground that dissipates the buildup of static electricity within a vehicle. However, not all materials that might be used in tire construction are necessarily electrically conductive. Rubber compositions that are electrically conductive are generally constructed from compounds having significant proportions of carbon black. Conversely, rubber compositions that are relatively nonconductive tend to have significantly larger amounts of silica relative to carbon black. In general, increasing the relative proportion of silica relative to carbon black decreases tire conductivity.
While silica-based compositions are generally poor conductors of electricity, the use of silica as a reinforcing material in the tread portion of a tire can provide increased braking ability under wet conditions and also can result in a tire having decreased rolling resistance. Accordingly, methods of providing a path of conductivity through an electrically insulating tire tread have been suggested. For example, see U.S. Pat. No. 5,937,926 (Powell), U.S. Pat. No. 6,220,319 and (Reuter), U.S. Pat. No. 6,269,854, which are hereby fully incorporated into this application for all purposes by reference thereto.
In recognition of the need for power generation and static electricity dissipation, in at tire environment, the provision of various electrically conductive paths in accordance with the present invention may offer dual functionality for vehicular applications in a tire for purposes in addition to providing a grounding path for static electricity buildup. Since it is desirable in many instances that electronic components associated with a tire structure be outfitted with some sort of power source, the buildup of static electricity within a tire is channeled and stored for powering such electronic components. Although known methods for power harvesting and for dissipation of static electricity associated with a tire structure have been respectively developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.